OPEN RELEASE of Version 3.7 of the
Gnu Xtal System of Crystallographic Programs

The Gnu Xtal System is a reasonably comprehensive,
modular suite of software oriented primarily towards small molecule
crystallography (with a smattering of powder and charge density
work). The software documented herein is directly descended from
the Xtal System (with only a minor name change) and thereby from
the original XRAY76 suite. It was conceived, created and maintained
for many years by Syd Hall (the originator of the
Crystallographic Information File (CIF)
at the University of Western Australia.
Numerous other developers have contributed
to this suite over the years.

One of the most novel features of Xtal is its use of the
RATionalized MACro (RATMAC) preprocessor to insulate the code base
from variations in F77 dialects and operating system specific
functionalities which were prevalent when the system was first
developed. Use of the RATMAC preprocessor also encouraged a coding
style in which almost every single line of code was documented,
aiding both the development and maintenance of the code base. The
modular design of the software and its use of archives for
conveying calculation results between different program modules
accessed by a nucleus of common IO routines has resulted in a very
robust and stable program suite and facilitated the development of
diverse calculation modules by many different authors. In fact an
earlier release of the the system contained more than 70 separate
calculation modules.

The Gnu Xtal System is then a reasonably extensive and
powerful set of portable crystallographic routines, with incredibly
well documented source code and more than 200 pages of usage notes,
eminently suited to the addition of new modules by new developers
(hint #1). It does however have two serious limitations. Firstly,
it is written in a language many people now find archaic, that
being fortran77, albeit tastefully wrapped in RATMAC and secondly,
it's size imparts a significant degree of inertia, such that it
cannot readily be modified to new programming styles and languages
(although the use of RATMAC might aid in such a transition if
sufficiently motivated people were dedicated to such a goal, hint
#2).

Consequently the past and present authors, developers and
maintainers of the the Xtal System present here, for your
crystallographic pleasure, the Gnu Xtal System, available
as an open source project, with the sincere belief that it is
useful, in the hope that community support may add renewed vigour
to the behemoth, but with the expectation that
Sourceforge may be
its twilight resting place, afore it's entombed by the sands of time, right alongside
The King of Kings.

The Gnu Xtal System is distributed under
the GNU General Public License.